1. Field of the Invention
This invention relates to determining the electrical condition of a battery.
2. Prior Art
Various apparatus using analog circuits are known to determine the state of charge of the battery. However, known meters have reduced accuracy because they do not take into account some significant parameters which affect the state of charge.
U.S. Pat. No. 3,886,442 issued to Chiku et al teaches a state of charge indicator circuit which employs the Peukert Equation in order to provide a measurement of the actual state of charge. The Peukert Equation relates the known fully charged battery capacity and the discharging battery current and is used to determine a compensated current related to the discharge current. An ampere-hour parameter corresponding to a known fully charged battery capacity is stored. An actual state-of-charge of the battery is determined by detecting the difference between an ampere-hour parameter integrated from the compensated current and the stored ampere-hour parameter. The patent discloses analog circuitry which does not take into account the discharge history of the battery, the recuperation effect of the battery, the regeneration efficiency of the battery and age compensation.
U.S. Pat. No. 4,289,836 issued to Lemelson teaches a battery recharging system including a microprocessor which receives as inputs battery voltage, current and temperature signals. The flow of electrical energy to recharge the battery is controlled in response to various battery conditions.
Accurate indication of the amount of charge remaining in the battery is particularly desirable in electric vehicle traction batteries. The available charge is directly related to the range available from the vehicle before a recharge. Because of the limited range of the electric vehicle and also because recharging facilities are not available on the road, an accurate fuel gauge is particularly desirable.
Also, known prior art coulomb meters for measuring the state of charge have inaccuracies because they do not take into account such variable factors as current variation, temperature, aging, recuperation and regeneration. These are some of the problems this invention overcomes.